River channels Venkatesh Merwade, University of Texas at Austin

Data for channels Bathymetry data for channels mainly include points with (x,y,z) attributes. Data can be collected using –Traditional methods (surveying) –Depth sounder (using a boat) –LIDAR ( Light Detection and Ranging) –SAR (Synthetic Aperture Radar), etc.

Data analysis Start with points Create surface from points Centerline/Thalweg Cross-sections ProfileLines Extract all the necessary information How do we do this…….

Defining a Thalweg Input Step 1Step 3Step 4 Output User defines an arbitrary centerline over the measurement points Thalweg tool creates a surface using the measurement points Normals are drawn at each vertex of the centerline to locate deepest points All the deepest points replace the vertices of the old centerline Final result is a 3D polyline defining the thalweg Densify the initial centerline to get more points Old vertices New vertices Step 2

Measure in ArcGIS A PolylineMZ can store m and z at each vertex along with x and y coordinates

Coordinate Transformation m is measure along the centerline r is distance across the river from the centerline Sinuous river becomes straight when transformed into (m,r) co-ordinates. x y m r

FishNet Points are interpolated in ArcMap to produce a continuous surface. FishNet is generated in ArcMap using the FishNet tool.

3D Visualization in ArcScene

Surface in transformed co-ordiantes Sinuous river Profile line and cross-sections Straightened river

Straightened River in 3D

Data back to x,y coordinates Original river in X,Y Profile lines and cross-sections in (x,y) created using FishNet in (m,r).

FishNet comparison Regular FishNet FishNet created in (r,m)

Profile Lines and Cross Sections in 3D Bird’s eye view!

Measurement pointsSurface Thalweg/CenterlineCross-sections ProfileLines Fishnet GIS for River Channels Develop generic ways to create all the channel features from measurement points.